Since copper appears to be an indispensable component of the angiogenesis process, the ability to induce new formation of capillaries in the cornea was tested for ceruloplasmin, the copper carrier of serum, for fragments of the ceruloplasmin molecule with and without copper, for heparin and for clycyl-2-histidyl-2-lysine bound or not to copper ions. The results showed that the 3 different molecules were all able to induce angiogenesis providing that they bound copper. Fragments of the ceruloplasmin molecule also induced angiogenesis, but only when copper was bound to the peptides. Highest efficiency at lowest dose was obtained in the corneal test when copper was bound to the ceruloplasmin molecule or a fragment thereof. The data are interpreted to indicate that copper ions are involved in the cascade of events conductive to angiogenesis but the carrier molecule may be of quite a different nature.